The conventional cyanidation/carbon in pulp process has been the main gold extraction method for decades. While cyanidation is effective for leaching gold from some carbonaceous or complex ores, there are serious environmental concerns associated with the use of cyanide in gold leaching processes. Thiosulfate is among the more successful alternative lixiviants for effective leaching of gold. An example of a thiosulfate leaching process for precious metal-containing materials is shown in U.S. Pat. No. 7,544,232.
Some oxide ores may be refractory in nature. They neither yield sufficient gold leaching in a thiosulfate leach system nor are leached as effectively compared to cyanide. Thiosulfate gold extraction from some oxide ores can be minimal. As oxide ores do not contain sulfides (or have very low levels of sulfide), the refractory nature cannot be mitigated in the same manner as for sulfide ores (e.g., by roasting, bio-oxidation or pressure oxidation).
There is a need for a thiosulfate leaching method to address the refractory nature of certain oxide ores in the thiosulfate leach system.